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Abstract:

According to the present invention, a plurality of video image data are
converted into individual spatial frequency information using Fourier
transformation. The individual spatial frequency information is provided
to a plurality of information display unit corresponding to the
individual spatial frequency information. The spatial frequency
information corresponding to the plurality of video image data is
displayed on the plurality of information display unit, light is
irradiated onto the plurality of information display unit using a
plurality of light sources corresponding to the plurality of information
display unit. The spatial frequency information that is displayed by the
plurality of information display unit is projected by using diffraction
light, and a plurality of video images are synthesized on projection
surfaces.

Claims:

1. A holographic projection method comprising:a Fourier transformation
step of converting a plurality of video image data into individual
spatial frequency information using Fourier transformation;an information
provision step of providing the individual spatial frequency information
to a plurality of information display unit corresponding to the
individual spatial frequency information;a display step of displaying the
spatial frequency information corresponding to the plurality of video
image data on the plurality of information display unit;an irradiation
step of irradiating light onto the plurality of information display unit
using a plurality of light sources corresponding to the plurality of
information display unit; anda projection step of projecting the spatial
frequency information displayed by the plurality of information display
unit using diffraction light and synthesizing a plurality of video images
onto projection surfaces.

3. The holographic projection method according to claim 2,wherein the
information display unit each are composed of a spatial light phase
modulator.

4. The holographic projection method according to claim 3,wherein the
plurality of spatial light phase modulators are disposed on the same
plane.

5. The holographic projection method according to claim 4,wherein the
plurality of spatial light phase modulators each are composed of a
reflecting spatial light phase modulator.

6. The holographic projection method according to claim 5,wherein the
plurality of spatial light phase modulators each include a mirror.

7. The holographic projection method according to claim 6, further
comprising:a light amount adjustment step of adjusting the amount of
light that is irradiated by the red light source, the green light source,
and the blue light source based on the video image data.

8. The holographic projection method according to claim 7,wherein the
amount of light that is incident from the red light source, the green
light source, and the blue light source is set to zero, while the spatial
frequency information is altered in the information display unit.

9. The holographic projection method according to claim 8,wherein the
adjustment of the light amount in the light amount adjustment step is
performed by controlling the red light source, the green light source,
and the blue light source.

10. The holographic projection method according to claim 1,wherein, in the
Fourier transformation step, the Fourier transformation is performed
after a random phase is added to the video image data.

11. The holographic projection method according to claim 10,wherein, in
the Fourier transformation step, a correction process based on phase
information depending on the optical system is executed on the spatial
frequency information including spatial light phase information obtained
by performing the Fourier transformation.

12. The holographic projection method according to claim 11,wherein, in
the Fourier transformation step, the correction process is executed based
on a distance between the spatial light phase modulator and projection
unit.

13. A holographic projection device comprising:a plurality of light
sources to irradiate light;data processing unit for converting a
plurality of video image data into individual spatial frequency
information using Fourier transformation; anda plurality of information
display unit which are provided to correspond to the plurality of light
sources and display the spatial frequency information,wherein the
plurality of information display unit are disposed such that diffraction
light, which is irradiated by the plurality of light sources and
modulated as the spatial phase information by the plurality of
information display unit, is synthesized as a projection video image on
projection surfaces.

14. The holographic projection device according to claim 13,wherein the
information display unit each are composed of a spatial light phase
modulator.

15. The holographic projection device according to claim 14,wherein the
plurality of spatial light phase modulators are disposed on the same
plane.

16. The holographic projection device according to claim 15,wherein the
plurality of spatial light phase modulators each are composed of a
reflecting spatial light phase modulator.

17. The holographic projection device according to claim 16,wherein the
plurality of spatial light phase modulators each include a mirror.

18. The holographic projection device according to claim 17,wherein the
plurality of light sources include at least a red light source, a green
light source, and a blue light source, andthe plurality of video image
data include at least red data, green data, and blue data.

19. The holographic projection device according to claim 18,wherein the
data processing unit handles the spatial frequency information as spatial
phase information by subjecting the video image data to the Fourier
transformation, after adding random phases to the video image data.

20. The holographic projection device according to claim 19, further
comprising:control unit for controlling the amount of light that is
irradiated by the red light source, the green light source, and the blue
light source based on the plurality of video image data.

21. The holographic projection device according to claim 13,wherein the
amount of light that is incident from the light sources is set to zero,
while the spatial frequency information is altered in the information
display unit.

22. The holographic projection device according to claim 13,wherein the
control unit controls the amount of light by controlling the light
sources.

23. The holographic projection device according to claim 22, further
comprising:unit for restricting illumination light from the light
sources, such that the illumination light is not irradiated onto an area
beyond an effective display range in the spatial light phase modulators.

24. The holographic projection device according to claim 13 or 23, further
comprising:unit for trapping zero-order light reflected on the spatial
light phase modulators.

25. The holographic projection device according to claim 13, further
comprising:zero-order light traps, each of which has an optical sensor
function capable of measuring intensity of light and traps zero-order
light reflected on the spatial light phase modulators,wherein the control
unit controls the amount of light that is irradiated by the light sources
based on output information of the zero-order light traps.

26. The holographic projection device according to claim 13, further
comprising:zero-order light traps, each of which has an optical sensor
function capable of measuring intensity of light,wherein the control unit
controls the amount of light that is irradiated by the light sources
based on output information of the zero-order light traps and the video
image data.

27. The holographic projection device according to claim 25,wherein the
control unit controls the amount of light irradiated by the light sources
based on a total light amount value of the amount of light in each scene
of a video image by the video image data.

28. The holographic projection device according to claim 27,wherein, when
T is defined as the number of bits of a gradation, M and N are defined as
the number of pixels vertically and the number of pixels horizontally in
each information display unit, respectively, and brightness of each pixel
is defined as represented by the following Equation 1, the control unit
calculates the total light amount value using the following Equation 2:
B ( x , y ) = 2 T ( Equation 1 ) H = y
= 1 M x = 1 N B ( x , y ) ( Equation 2
) ##EQU00005##

29. The holographic projection device according to claim 28,wherein, when
H is defined as a total light amount value of a projected video image, S
is defined as a light amount of zero-order light, and K is defined as a
proportionality coefficient, the control unit controls the amount of
light irradiated by the light sources based on a value calculated using
the following Equation 3: F = H K + S ( Equation 3 )
##EQU00006##

30. The holographic projection device according to claim 13,wherein a
calculation precision of the data processing unit is at least 12 bits or
more.

31. The holographic projection device according to claim 13,wherein the
data processing unit converts video image data into spatial frequency
information after added different random phases to the video image data
in a subframe unit.

32. A holographic projection method comprising:a Fourier transformation
step of converting video image data into spatial phase information using
Fourier transformation after added different random phases to the video
image data in a subframe unit;an information provision step of providing
the spatial phase information to information display unit;a display step
of displaying spatial phase information corresponding to the video image
data as a phase distribution on the information display unit;an
irradiation step of irradiating light onto the information display unit
using light sources;a light amount adjustment step of controlling drivers
of the light sources to adjust the amount of light irradiated by the
light sources based on the video image data; anda projection step of
projecting diffraction light, which is irradiated by the light sources
and modulated as the spatial phase information by the information display
unit, onto projection unit.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This is a Continuation Application of PCT Application No.
PCT/JP2008/053283, filed Feb. 26, 2008, which was published under PCT
Article 21(2) in Japanese.

[0002]This application is based upon and claims the benefit of priority
from prior Japanese Patent Application No. 2007-053110, filed Mar. 2,
2007, the entire contents of which are incorporated herein by reference.

[0006]In general, examples of a projection device that projects a video
image onto a screen include a projection device using transmission-type
liquid crystal (LC), a projection device using reflecting liquid crystal
(liquid crystal on silicon [LCOS]), and a projection device using a
digital micromirror device (DMD).

[0007]For example, in the projection device using liquid crystal, a video
image is projected onto a screen as follows. That is, first, a video
image that a user desires to project is displayed on liquid crystal in
accordance with video image data. Then, the liquid crystal is illuminated
by illumination light and transmission light or reflection light is
projected by a projection lens, and the video image displayed on the
liquid crystal is displayed on a screen to be enlarged.

[0008]In the projection device using a DMD, a video image is displayed on
the DMD by turning on/off the micromirrors which constitutes the DMD and
correspond to pixels in accordance with video image date and then the
video image date is projected onto a screen by a projection lens.

[0009]The above-described projection devices adopt a method in which a
video image is displayed on an image display element, e.g; liquid
crystal, at a time and the displayed video image is projected to be
enlarged by the projection lens. Accordingly, the above-described
projection devices each include a light source, an illumination optical
system, an image display element, and a projection lens.

[0010]In addition, in a color sequencing expression, a color filter that
changes a color of a light source is further required. In a method using
a plurality of image display elements for each color, a color
separation/synthesis optical system that is provided around the image
display elements is further required.

[0011]In general, an incoherent light source, such as a high pressure
mercury lamp, is used as a light source. Therefore, a complicated
illumination optical system is needed to efficiently and uniformly
illuminate light to the image display elements using the light source.

[0012]For a color conversion, a color filter needs to be provided and a
color synthesis/separation optical system needs to be provided around the
excessively complicated image display elements.

[0013]In view of such circumstances, a projection device using a spatial
light phase modulator (SPM), which is shown in FIG. 7, is suggested. For
example, this type of projection device is disclosed in detail in WO
2005/059881A3.

[0014]That is, in the projection device that is disclosed in WO
2005/059881A3, as shown in FIG. 7, linearly polarized light from a light
source (laser) 100 is incident on a polarized beam splitter (PBS) 102,
reflected on the PBS 102, and incident on an LCOS 104 that is the SPM. In
addition, a λ/4 plate (not shown) is provided between the PBS 102
and the LCOS 104.

[0015]Diffraction light 105 is subjected to phase modulation by the LCOS
104 in accordance with video image data and then reflected. The
diffraction light 105 passes through the λ/4 plate again, is
transmitted through the PBS 102, and is projected onto a screen 108
through a projection lens 106. In this case, a binary modulation of a
phase difference 7 is obtained according to whether or not the phase
modulation is performed by the LCOS 104. Meanwhile, zero-order light 107
is not incident on the projection lens 106.

[0016]As such, for example, in WO 2005/059881A3, a small-sized projection
device is disclosed, which uses a simple illumination optical system and
includes a simple projection lens.

[0017]The method that is disclosed in WO 2005/059881A3 is a method that
projects a video image using diffraction. In this case, the brightness of
the projected video image is determined based on diffraction efficiency
of a spatial light phase modulator. For example, in the case of the
binary modulation of the phase difference π, diffraction efficiency is
approximately 40%. In addition, if the amount of phase modulation is
changed minutely, it is possible to improve diffraction efficiency. In
addition, if the amount of phase modulation is continuously changed, the
diffraction efficiency ideally reaches 100%.

[0018]In addition, the total amount of the diffracted light with respect
to the light source accounts for a predetermined ratio. Meanwhile, a
bright scene and a dark scene exist in the video image, and the total
amount of light is changed. Accordingly, when the brightness of the light
source is constant, for example, an originally dark scene of a video
image may be displayed brightly. In view of such circumstances, the total
amount of brightness of each scene needs to be calculated for each scene
based on video image data, and the amount of light that is incident on
the SPM needs to be adjusted such that the brightness of each scene is
appropriately maintained with respect to a scene having the maximum
brightness.

[0019]As a technology that may be used to solve the above-described
problems, for example, U.S. Pat. No. 5,589,955 discloses the following
technology. In the case that characters of dot patterns are drawn, since
the number of dots is different for each character, an output of a laser
that is a light source is increased or decreased to make brightness of
each character the same by counting the number of the dots.

[0020]In addition, in order to perform color video image display,
generally, a red image, a blue image, and a green image need to be
synthesized. Accordingly, a complicated optical system is needed.

BRIEF SUMMARY OF THE INVENTION

[0021]In general, in order to obtain a color video image in a projection
device, a complicated optical system is needed.

[0022]The prevent invention has been made to solve the above-described
problems, and it is an object of the present invention to provide video
image display using a holographic projection method and a holographic
projection device in which a complicated optical system, such as a
synthesis prism, is not needed by utilizing a characteristic using a
spatial light phase modulator, thereby achieving a simplified structure.

[0023]According to a first aspect of the invention, there is provided a
holographic projection method comprising:

[0026]a display step of displaying the spatial frequency information
corresponding to said plurality of video image data on said plurality of
information display means;

[0027]an irradiation step of irradiating light onto said plurality of
information display means using a plurality of light sources
corresponding to said plurality of information display means; and

[0028]a projection step of projecting the spatial frequency information
displayed by said plurality of information display means using
diffraction light and synthesizing a plurality of video images onto
projection surfaces. As a result, it is possible to realize a holographic
projection method using a small device.

[0029]According to a second aspect of the invention, there is provided the
holographic projection method according to the first aspect,

[0030]wherein said plurality of light sources include a red light source,
a green light source, and a blue light source, and

[0032]According to a third aspect of the invention, there is provided the
holographic projection method according to the second aspect,

[0033]wherein the information display means each are composed of a spatial
light phase modulator. As a result, it is possible to provide a
holographic projection method that has excellent light utilization
efficiency.

[0034]According to a fourth aspect of the invention, there is provided the
holographic projection method according to the third aspect,

[0035]wherein said plurality of spatial light phase modulators are
disposed on the same plane. As a result, it is possible to provide a
method in which color display can be realized without using a color
synthesis prism.

[0036]According to a fifth aspect of the invention, there is provided the
holographic projection method according to the fourth aspect,

[0037]wherein said plurality of spatial light phase modulators each are
composed of a reflecting spatial light phase modulator. As a result, it
is possible to provide a display method in which high diffraction
efficiency can be realized and bright display is enabled.

[0038]According to a sixth aspect of the invention, there is provided the
holographic projection method according to the fifth aspect,

[0039]wherein said plurality of spatial light phase modulators each
include a mirror. As a result, it is possible to provide a display method
in which higher light utilization efficiency can be obtained and brighter
display is enabled.

[0040]According to a seventh aspect of the invention, there is provided
the holographic projection method according to the sixth aspect, further
comprising:

[0041]a light amount adjustment step of adjusting the amount of light that
is irradiated by the red light source, the green light source, and the
blue light source based on the video image data. As a result, it is
possible to provide display having excellent color balance.

[0042]According to an eighth aspect of the invention, there is provided
the holographic projection method according to the seventh aspect,

[0043]wherein the amount of light that is incident from the red light
source, the green light source, and the blue light source is set to zero,
while the spatial frequency information is altered in the information
display means. As a result, unnecessary diffraction light can be removed
and display having excellent contrast can be provided.

[0044]According to a ninth aspect of the invention, there is provided the
holographic projection method according to the eighth aspect,

[0045]wherein the adjustment of the light amount in the light amount
adjustment step is performed by controlling the red light source, the
green light source, and the blue light source. As a result, it is
possible to provide display means that has excellent color balance and
excellent contrast without individually including light amount control
means.

[0046]According to a tenth aspect of the invention, there is provided the
holographic projection method according to the first aspect,

[0047]wherein, in the Fourier transformation step, the Fourier
transformation is performed after random phases are added to the video
image data. As a result, it is possible to use phase-modulation
diffraction having excellent diffraction efficiency and to realize bright
display.

[0048]According to an eleventh aspect of the invention, there is provided
the holographic projection method according to the tenth aspect,

[0049]wherein, in the Fourier transformation step, a correction process
based on phase information depending on the optical system is executed on
the spatial frequency information including spatial light phase
information obtained by performing the Fourier transformation. As a
result, it is possible to increase a degree of freedom of optical
arrangement.

[0050]According to a twelfth aspect of the invention, there is provided
the holographic projection method according to the eleventh aspect,

[0051]wherein, in the Fourier transformation step, the correction process
is executed based on a distance between the spatial light phase modulator
and projection means. As a result, it is possible to provide projection
means in which it is possible to cope with a change in projection
distance and to freely change a projection distance without using a
projection lens and focusing thereof.

[0052]According to a thirteenth aspect of the invention, there is provided
a holographic projection device comprising:

[0053]a plurality of light sources to irradiate light;

[0054]data processing means for converting a plurality of video image data
into individual spatial frequency information using Fourier
transformation; and

[0055]a plurality of information display means which are provided to
correspond to said plurality of light sources and display the spatial
frequency information,

[0056]wherein said plurality of information display means are disposed
such that diffraction light, which is irradiated by said plurality of
light sources and modulated as the spatial phase information by said
plurality of information display means, is synthesized as a projection
video image on projection surfaces. As a result, it is possible to
provide a holographic projection device that does not need a color
synthesis prism.

[0057]According to a fourteenth aspect of the invention, there is provided
the holographic projection device according to the thirteenth aspect,

[0058]wherein the information display means each are composed of a spatial
light phase modulator. As a result, it is possible to provide a
projection device that has high light utilization efficiency.

[0059]According to a fifteenth aspect of the invention, there is provided
the holographic projection device according to the fourteenth aspect,

[0060]wherein said plurality of spatial light phase modulators are
disposed on the same plane. As a result, adjustment can be easily made.

[0061]According to a sixteenth aspect of the invention, there is provided
the holographic projection device according to the fifteenth aspect,

[0062]wherein said plurality of spatial light phase modulators each are
composed of a reflecting spatial light phase modulator. As a result, it
is possible to realize a projection device in which high diffraction
efficiency can be obtained by adopting a plurality of reflecting spatial
light phase modulators and a bright projection video image can be
obtained.

[0063]According to a seventeenth aspect of the invention, there is
provided the holographic projection device according to the sixteenth
aspect,

[0064]wherein said plurality of spatial light phase modulators each
include a mirror. As a result, it is possible to realize a projection
device in which higher light utilization efficiency can be obtained and
bright display can be achieved.

[0065]According to an eighteenth aspect of the invention, there is
provided the holographic projection device according to the seventeenth
aspect,

[0066]wherein said plurality of light sources include at least a red light
source, a green light source, and a blue light source, and

[0067]said plurality of video image data include at least red data, green
data, and blue data. As a result, it is possible to realize color
display.

[0068]According to a nineteenth aspect of the invention, there is provided
the holographic projection device according to the eighteenth aspect,

[0069]wherein the data processing means handles the spatial frequency
information as spatial phase information by subjecting the video image
data to the Fourier transformation, after adding random phases to the
video image data. As a result, it is possible to achieve display using
phase diffraction having high diffraction efficiency. As a result, it is
possible to realize a projection device in which light utilization
efficiency is high and a bright projection video image can be obtained.

[0070]According to a twentieth aspect of the invention, there is provided
the holographic projection device according to the nineteenth aspect,
further comprising:

[0071]control means for controlling the amount of light that is irradiated
by the red light source, the green light source, and the blue light
source based on said plurality of video image data. As a result, it is
possible to display a video image having excellent color balance.

[0072]According to a twenty-first aspect of the invention, there is
provided the holographic projection device according to the thirteenth
aspect,

[0073]wherein the amount of light incident from the light sources is set
to zero, while the spatial frequency information is altered in the
information display means. As a result, unnecessary diffraction light can
be prevented from being generated and a video image having high contrast
can be provided.

[0074]According to a twenty-second aspect of the invention, there is
provided the holographic projection device according to the thirteenth
aspect,

[0075]wherein the control means controls the amount of light by
controlling the light sources. As a result, a light amount can be
controlled without using a light intensity modulator and a video image
having excellent color balance and excellent contrast can be easily
provided.

[0076]According to a twenty-third aspect of the invention, there is
provided the holographic projection device according to the twenty-second
aspect, further comprising:

[0077]means for restricting illumination light from the light sources,
such that the illumination light is not irradiated onto an area beyond an
effective display range in the spatial light phase modulators. As a
result, it is possible to prevent unnecessary stray light from being
generated and to provide a video image having excellent contrast.

[0078]According to a twenty-fourth aspect of the invention, there is
provided the holographic projection device according to the thirteenth or
twenty-third aspect, further comprising:

[0079]means for trapping zero-order light reflected on the spatial light
phase modulators. As a result, unnecessary stray light can be prevented
from overlapping a video image, and a high-definition video image can be
provided.

[0080]According to a twenty-fifth aspect of the invention, there is
provided the holographic projection device according to the thirteenth or
twenty-third aspect, further comprising:

[0081]zero-order light traps, each of which has an optical sensor function
capable of measuring intensity of light and traps zero-order light
reflected on the spatial light phase modulators,

[0082]wherein the control means controls the amount of light that is
irradiated by the light sources based on output information of the
zero-order light traps. As a result, unnecessary stray light can be
prevented from being generated, a video image having high contrast can be
provided, and a high-definition video image having excellent color
balance can be provided.

[0083]According to a twenty-sixth aspect of the invention, there is
provided the holographic projection device according to the thirteenth or
twenty-third aspect, further comprising:

[0084]zero-order light traps, each of which has an optical sensor function
capable of measuring intensity of light,

[0085]wherein the control means controls the amount of light, that is
irradiated by the light sources, based on output information of the
zero-order light traps and the video image data. As a result, unnecessary
stray light can be prevented from being generated and a video image
having high contrast can be provided. Moreover, brightness control can be
realized in consideration of a change in diffraction efficiency due to a
difference between video images in a spatial light phase modulator so
that minute brightness control and color balance control can be realized
and an impressive video image can be provided.

[0086]According to a twenty-seventh aspect of the invention, there is
provided the holographic projection device according to the twenty-fifth
or twenty-sixth aspect,

[0087]wherein the control means controls the amount of light irradiated by
the light sources based on a total light amount value of the amount of
light in each scene of a video image by the video image data. As a
result, it is possible to realize accurate brightness reproduction.

[0088]According to a twenty-eighth aspect of the invention, there is
provided the holographic projection device according to the
twenty-seventh aspect,

[0089]wherein, when T is defined as the number of bits of a gradation, M
and N are defined as the number of pixels of each information display
means in vertical and horizontal directions respectively, and brightness
of each pixel is defined as represented by the following Equation 1, the
control means calculates the total light amount value using the following
Equation 2:

[0090]As a result, it is possible to accurately calculate the total light
amount value.

[0091]According to a twenty-ninth aspect of the invention, there is
provided the holographic projection device according to the twenty-eighth
aspect,

[0092]wherein, when H is defined as a total light amount value of a
projected video image, S is defined as a light amount of zero-order
light, and K is defined as a proportionality coefficient, the control
means controls the amount of light irradiated by the light sources based
on a value calculated using the following Equation 3:

F = H K + S ( Equation 3 ) ##EQU00002##

[0093]As a result, it is possible to achieve brightness control based on
an accurate value.

[0094]According to a thirtieth aspect of the invention, there is provided
the holographic projection device according to the thirteenth or
twenty-ninth aspect,

[0095]wherein a calculation precision of the data processing means is at
least 12 bits or more. As a result, it is possible to represent a video
image having a sufficient gradation.

[0096]According to a thirty-first aspect of the invention, there is
provided the holographic projection device according to the thirteenth or
thirtieth aspect,

[0097]wherein the data processing means converts video image data into
spatial frequency information after adding different random phases to the
video image data in a subframe unit. As a result, it is possible to
provide a clear video image that does not have speckle noise.

[0098]According to a thirty-second aspect of the invention, there is
provided a holographic projection method comprising:

[0099]a Fourier transformation step of converting video image data into
spatial phase information using Fourier transformation after adding
different random phases to the video image data in a subframe unit;

[0103]a light amount adjustment step of controlling drivers of the light
sources to adjust the amount of light irradiated by the light sources
based on the video image data; and

[0104]a projection step of projecting diffraction light, which is
irradiated by the light sources and modulated as the spatial phase
information by the information display means, onto projection means. As a
result, it is possible to provide a clear video image that does not have
speckle noise.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0105]FIG. 1 is a block diagram illustrating an example of the
configuration of a holographic projection device according to an
embodiment of the invention.

[0106]FIG. 2 is a block diagram illustrating an example of the
configuration of a holographic projection device according to an
embodiment of the invention.

[0107]FIG. 3 is a diagram illustrating a sequence for converting video
image data into information displayed on an MMD in a holographic
projection device according to an embodiment of the invention.

[0108]FIG. 4 is a diagram illustrating a timing chart that represents a
relationship between an operation of an SPM and light-emitting operations
of laser diodes for red, green, and blue by the same time base t, when
color display is performed on a projection video image by performing
light source control, in a holographic projection device according to an
embodiment of the invention.

[0109]FIG. 5A is a diagram illustrating the configuration of a holographic
projection device according to an embodiment of the invention disposed at
a normal location, when viewed from an upper side.

[0110]FIG. 5B is a diagram illustrating the configuration of a holographic
projection device according to an embodiment of the invention disposed at
a normal location, when a peripheral portion of an SPM for blue in the
holographic projection device is viewed from a viewing direction E shown
in FIG. 5A.

[0111]FIG. 6A is a cross-sectional view illustrating a reflecting MMD in a
holographic projection device according to an embodiment of the
invention.

[0112]FIG. 6B is a cross-sectional view illustrating a reflecting MMD in a
holographic projection device according to an embodiment of the
invention.

[0113]FIG. 7 is a diagram illustrating the configuration of a projector
that uses a conventionally suggested SPM.

DETAILED DESCRIPTION OF THE INVENTION

[0114]Hereinafter, one embodiment of the invention will be described with
reference to the accompanying drawings.

[0115]FIG. 1 is a diagram illustrating an example of the configuration of
a holographic projection device according to an embodiment of the
invention. As shown in the drawing, the holographic projection device
according to this embodiment includes a light source 2r for red that is
composed of a laser diode (LD) and functions as a red light source, a
light source 2g for green that is composed of an LD and functions as a
green light source, and a light source 2b for blue that is composed of an
LD and functions as a blue light source, and reflecting SPMs 4r, 4g, and
4b that correspond to the light sources for the individual colors.

[0116]In this case, light generated by the light source 2r for red, the
light source 2g for green, and the light source 2b for blue is incident
on the SPMs 4r, 4g, and 4b correspond to the individual light sources,
and diffracted based on information written in the SPMs 4r, 4g, and 4b,
to be projected onto a screen 6. In addition, on the screen 6,
information projected by the light source 2r for red, the light source 2g
for green, and the light source 2b for blue is synthesized and reproduced
as a color video image.

[0117]That is, in this embodiment, the light emitted from the light source
2r for red, the light source 2g for green, and the light source 2b for
blue is not synthesized by, for example, a color synthesis prism to
project a color video image. Instead, combinations of the light source 2r
for red, the light source 2g for green, and the light source 2b for blue
and the SPMs 4r, 4g, and 4b are arranged on the same plane in parallel to
each other, as shown in FIG. 1, thereby realizing color display.

[0118]In this embodiment, as described above, a holographic projection
device, which can obtain a projection video image of color display by
means of the very simple configuration, is realized.

[0119]In addition, illumination light is divergent light, and irradiated
by the light source 2r for red, the light source 2g for green, and the
light source 2b for blue from an oblique upper side of the SPMs 4r, 4g,
and 4b, as shown in FIGS. 1 and 2.

[0120]In this embodiment, a reflecting SPM is used as each of the SPMs 4r,
4g, and 4b. Specifically, in the reflecting SPM, a micromirror spatial
light phase modulator (magic mirror device [MMD]), which will be
described in detail below, is used. In addition, the LCOS may be used as
the SPMs 4r, 4g, and 4b.

[0121]In addition, the holographic projection device according to this
embodiment can be realized using the configuration of the device shown in
FIG. 2. Hereinafter, a difference from the device configuration shown in
FIG. 1 will be mainly described.

[0122]That is, in the example of the device configuration shown in FIG. 2,
the holographic projection device includes a light source 2r for red that
is composed of an LD and functions as a red light source, a light source
2g for green that is composed of an LD and functions as a green light
source, a light source 2b for blue that is composed of an LD and
functions as a blue light source, converging lenses 3r, 3g, and 3b that
converge light emitted from the light sources for the individual colors
respectively, reflecting SPMs 4r, 4g, and 4b that correspond to the light
sources for the individual colors, and zero-order light traps 8r, 8g, and
8b that capture zero-order light generated by the SPMs 4r, 4g, and 4b.

[0123]In this case, the light emitted from the light source 2r for red,
the light source 2g for green, and the light source 2b for blue is
incident on the SPMs 4r, 4g, and 4b corresponding to the individual light
sources through the converging lenses 3r, 3g, and 3b corresponding to the
individual light sources, diffracted based on information written in the
SPMs 4r, 4g, and 4b, and projected onto the screen 6.

[0124]In addition, on the screen 6, the information projected by the light
source 2r for red, the light source 2g for green, and the light source 2b
for blue is synthesized, and reproduced as a color video image.

[0125]In addition, the zero-order light generated by the SPMs 4r, 4g, and
4b is captured by the zero-order light traps 8r, 8g, and 8b. As a result,
unnecessary stray light can be prevented from being generated and a video
image having excellent contrast can be projected.

[0126]Next, a sequence for converting video image data into the
information displayed on the MMD in the SPMs 4r, 4g, and 4b will be
described with reference to FIG. 3. The process in each step shown in
FIG. 2 is executed by control means (not shown) that is included in the
holographic projection device according to this embodiment.

[0127]In this embodiment, phase information obtained by Fourier
transformation of video image date is displayed on the SPMs 4r, 4g, and
4b. Illumination light is irradiated onto the SPMs 4r, 4g, and 4b, and
light diffracted by the SPMs 4r, 4g, and 4b is projected onto the screen
6.

[0128]In addition, it is preferable that the illumination light from the
light source 2 be not irradiated beyond an effective display range of
phase information in the SPMs 4r, 4g, and 4b.

[0129]First, video image data of a video image that is to be projected is
obtained. In this case, the video image data is subjected to Fourier
transformation to be converted into spatial frequency distribution
information. However, when the video image data is subjected to Fourier
transformation as it is, a spatial phase distribution and a spatial
intensity distribution may be generated. For this reason, it is not
possible to diffract light by a phase modulation with excellent
diffraction efficiency.

[0131]If the random phase information is added to the video image data, it
means that a phase value different for each pixel is added to intensity
information of each pixel of one frame of the video image data. For
example, it means that a value of 128+j is obtained, when a value of the
intensity of an arbitrary pixel is 128. In this case, j is a unit
imaginary number.

[0132]The human eye (and image sensors) can sense only the intensity of
light. Accordingly, a phase represented in an imaginary unit does not
have a practical meaning, but has an important meaning for calculation.
That is, a phase is included even in pure intensity information after
subjecting video image data to Fourier transformation.

[0133]If random phases are added to the video image data in advance,
values of intensity portion after Fourier transformation can be averaged
over the entire spatial frequency surface, and the intensity can be
equalized over the entire frequency surface. That is, it is possible to
obtain pure phase information having no change in intensity.

[0134]In the case where the video image data is subjected to Fourier
transformation, after taking the root of a value of the signal intensity
of the video image data, that is, converting the video image data into
amplitude information, Fourier transformation is preferably performed. In
addition, the random phase is preferably added to the amplitude
information.

[0135]In this way, the video image data can be converted into phase
information. In other words, the spatial frequency information can be
converted into phase information, that is, spatial phase information.
Since this method is a technology that is conventionally known as a
kinoform, the detailed description thereof will be omitted herein. If a
random phase is made to overlap video image data, the intensity on the
spatial frequency distribution can be averaged and the video image data
can be satisfied by only phase information.

[0137]As described above, the video image data where the random phase
overlaps and Fourier transformation is performed is converted into
spatial phase information that is composed of only phase information.
Then, a correction process (correction process step S3) based on optical
arrangement is executed on the spatial phase information and the
corrected spatial phase information is input to an SPM driver. In this
case, the SPM driver is a driver that generates a driving signal to drive
the SPMs 4r, 4g, and 4b.

[0138]When the video image data has a gradation of A bits, the transform
calculation is preferably made based on the number of bits that maintains
the gradation. That is, in this case, it is preferable that effective
digits of a Fourier transformation result be A bits or more. Accordingly,
even in the mid-calculation, a precision where effective digits are A
bits or more is minimally needed.

[0139]In the related art, the gradation of the digital video image is 8
bits, and the calculation is also made based on the corresponding number
of bits. In recent years, however, a gradation of 12 bits or more is
required. Accordingly, a calculation precision of 12 bits or more,
including digital data of an original video image, is needed.

[0140]In this case, as shown in FIGS. 1 and 2, the illumination light is
convergent light and irradiated from the oblique upper side of the SPMs
4r, 4g, and 4b. In addition, spatial phase information for projecting a
video image in spreading on a front side with respect to said
illumination light is provided to the SPMs 4r, 4g, and 4b.

[0141]That is, after providing a phase (Step S1) when the video image data
is subjected to Fourier transformation, spatial phase information that
depends on the corresponding optical system is provided to the SPMs 4r,
4g, and 4b, such that the video image is projected in a desired
direction. The projection (holographic projection) method that uses
diffraction in this embodiment is different from a method that controls
brightness of each pixel to form an image. That is, in the projection
method, brightness of each pixel is displayed on a screen by diffraction
of light on the front side of the SPMs 4r, 4g, and 4b.

[0142]In addition, a driving signal is applied to the SPMs 4r, 4g, and 4b
by the SPM driver, such that spatial phase information which corresponds
to a video image to be projected onto the SPMs 4r, 4g, and 4b, appears as
a phase distribution (SPM driver control step S4).

[0143]Meanwhile, when the diffraction efficiency of the SPMs 4r, 4g, and
4b is constant, both a video image of a dark scene and a video image of a
bright scene may become a video image that has the same brightness.
Accordingly, in accordance with the total amount of the light amounts of
the video images, the amount of light that is incident on the SPMs 4r,
4g, and 4b needs to be changed as follows.

[0144]That is, the total amount (the total light amount value; a
calculation method thereof will be described in detail below) of
brightness of each scene in the projected video image is calculated, and
the amount of light to be incident on the SPMs 4r, 4g, and 4b is
controlled such that the brightness of each scene becomes appropriate
(light source driver control step S5). In Step S5, the drivers of the
light source 2r for red, the light source 2g for green, and the light
source 2b for blue are controlled based on the video image data.

[0145]In addition, in the case of the configuration of the device that is
shown in FIG. 2, the amount of light by the light source 2r for red, the
light source 2g for green, and the light source 2b for blue may be
controlled based on output information of the zero-order light traps 8r,
8g, and 8b. The zero-order light traps 8r, 8g, and 8b each may be
composed of an optical sensor, and the amount of light by the light
source 2r for red, the light source 2g for green, and the light source 2b
for blue may be controlled based on the output information of the
zero-order light trap and the video image data.

[0146]FIG. 4 shows an aspect of light source control in a holographic
projection device according to this embodiment. FIG. 4 is a diagram
illustrating a timing chart that represents a relationship between
operations of SPMs 4r, 4g, and 4b and light-emitting operations of light
sources 2r, 2g, and 2b for red, green, and blue by the same time base t.

[0147]In this case, in a holographic projection device according to this
embodiment, as shown in FIG. 1, a plurality of light sources and the SPMs
correspond to each other. In addition, the holographic projection device
simultaneously makes the light source 2r for red, the light source 2g for
green, and the light source 2b for blue emit light, thereby performing
color display. While the SPMs 4r, 4g, and 4b alter individual color
information, as shown in FIG. 4, all of the light sources, that is, the
light source 2r for red, the light source 2g for green, and the light
source 2b for blue are turned off. Instead of turning off the light
sources so as not to emit light, a light shielding unit may be installed
so as not to make light from the light sources be incident.

[0148]In regards to the light amount control, light emission intensity of
the light source 2r for red, the light source 2g for green, and the light
source 2b for blue is adjusted based on video image data, as described
above. In addition, a light intensity modulator may be installed in the
middle of an optical path of light that is irradiated by the light source
2r for red, the light source 2g for green, and the light source 2b for
blue.

[0149]Meanwhile, when the ideal diffraction efficiency of the SPMs 4r, 4g,
and 4b is 100%, the amount F of light that is represented by a sum of
amounts of light incident on the individual SPMs 4r, 4g, and 4b is
proportional to the total light amount value H of one scene in the
projection video image. This is applicable to the case where diffraction
efficiency of the SPMs is constant. Here, if brightness of a pixel of a
gradation T-bit at address (x, y) is defined as B(x,y), the following
Equation 7 is obtained.

B(x,y)≦2T (Equation 7)

[0150]From Equation 7, the following Equation 8 is obtained and the total
light amount value H of one scene can be calculated.

H = y = 1 M x = 1 N B ( x , y ) (
Equation 8 ) ##EQU00003##

[0151]In this case, M and N denote the number of pixels vertically and the
number of pixels horizontally, respectively. For example, in the case of
a high-definition TV, the conditions M=1080 and N=1920 are applied. If
the brightness of the light source is controlled based on the total light
amount value H, appropriate brightness in each scene of video images is
obtained. As a result, considerably clear video images can be reproduced
to be dark in a dark scene of a video image and bright in a bright scene
of a video image.

[0152]In addition, diffraction efficiency may be changed depending on a
video image. In this case, in order to accurately perform a correction
process, the amount S of zero-order light may be measured, and brightness
of the light source may be controlled such that a value obtained by
subtracting the amount S of light from the amount F of incident light
represented by a sum of amounts of light incident on the SPMs 4r, 4g, and
4b is proportional to the total light amount value H. That is, if a
proportionality coefficient is defined as K, the following Equation 9 is
obtained.

K(F-S)=H (Equation 9)

[0153]That is, the brightness of the light source may be controlled such
that the amount of incident light becomes the amount of incident light
represented by the following Equation 10.

F = H K + S ( Equation 10 ) ##EQU00004##

[0154]Hereinafter, a method of reducing noise in a holographic projection
method and a holographic projection device according to this embodiment
will be described. In WO 2005/059881A3, the reduction of noise is
described as follows.

[0155]That is, according to the contents that are disclosed in WO
2005/059881A3, examples of noise include systematic noise and
non-systematic noise.

[0156]Further, according to the contents, systematic noise include noise
due to an error that occurs at the time of reproducing a phase by the SPM
and noise due to irregularity, and non-systematic noise include noise due
to an error that occurs at the time of executing an algorithm and noise
due to a binarization error.

[0157]In addition, as means for dealing with non-systematic noise, there
is suggested a technology using a subframe as a technology that repeats
one frame plural times as follows.

[0158]That is, for example, if time of one frame is 1/60 second, the
corresponding time is divided into 1/180 second and the same video image
is displayed three times. In this way, a method in which noise is
averaged and reduced is disclosed in WO 2005/059881A3. In addition,
according to the contents disclosed in WO 2005/059881A3, since noise
occurs by a device, a process of adding a random phase to video image
data does not need to be repeated.

[0159]However, if the above-described various types of noise are reduced,
speckle noise become highly visibles. Speckle noise conspicuously occurs
when a laser is used, in particular. That is in a video image projected
onto a screen where light from pixels around each pixel interferes with
light from each pixel, speckle noise occurs when granular noise having
high contrast is generated on the retina of a person who views the
corresponding video image.

[0160]This speckle noise is generated when coherence exists in the light
source used in projection. Accordingly, in speckle noise, if a wave
surface is the same, the same speckle is reproduced. In the case of a
video image where a projected video image gradually changes or a still
picture, speckle noise is conspicuously observed. For this reason, in the
case of the video image where the projected video image gradually changes
or the still picture, it is necessary to change a phase of projection
light without changing the projected video image.

[0161]In view of such circumstances, in this embodiment, one frame is
divided into subframes (for example, one frame corresponding to 1/60
second is divided into subframes corresponding to 1/120 second), and even
in each subframe, a random phase different from that of another subframe
as a random phase added to video image data is added to the corresponding
subframe. By this process, a shape of the generated speckle is changed
and averaged, thereby reducing noise and displaying a high-definition
video image. That is, one frame is divided into subframes, and different
random phase data is added to the same video image data and the
corresponding subframe is repeated.

[0162]Meanwhile, like the holographic projection device according to this
embodiment, in a holographic projection device that includes the three
light sources and the SPMs corresponding to the three light sources, for
example, the device configuration shown in FIG. 5 can be adopted.

[0163]FIG. 5A is a diagram illustrating the configuration of a holographic
projection device (disposed at a normal location) according to an
embodiment of the invention that includes three light sources and SPMs
corresponding to the three light sources, when viewed from an upper side.
FIG. 5B is a diagram illustrating the configuration of a holographic
projection device (disposed at a normal location) according to an
embodiment of the invention that includes three light sources and SPMs
corresponding to the three light sources, when a peripheral portion of an
SPM for blue in the holographic projection device is viewed from a
viewing direction E shown in FIG. 5A.

[0164]The holographic projection device shown in FIGS. 5A and 5B includes
an LD for red (not shown in FIGS. 5A and 5B) that functions as a red
light source, an LD 12 for green (not shown in FIGS. 5A and 5B) that
functions as a green light source, an LD for blue (not shown in FIG. 5A)
that functions as a blue light source, collimators 26a, 26b, and 26c that
correspond to the light sources for the individual colors, respectively,
total reflection prisms 27a, 27b, and 27c that correspond to the light
sources for the individual colors, respectively, reflecting SPMs 28a,
28b, and 28c that correspond to the light sources for the individual
colors, respectively, traps 29a, 29b, and 29c functioning as light
shielding members that correspond to the light sources for the individual
colors, respectively, a color synthesis prism 20 that synthesizes
diffraction light of the individual colors, and a projection lens 22.

[0165]In this case, in regards to the zero-order light, as shown in FIG.
5B, light emitted from the LD 12 for blue is reflected on the total
reflection prism 27c, collimated by the collimator 26c, and incident on
the SPM 28c for blue. In this case, zero-order light passes through the
collimator 26c again, is reflected on the total reflection prism 27c, and
reaches the trap 29c. In this way, the unnecessary zero-order light is
removed.

[0166]Meanwhile, among light irradiated by the LD 12 for blue, the light
diffracted by a spatial phase modulation for a blue video image displayed
on the SPM 28c for blue becomes an approximately collimated light beam by
the collimator, and is then incident on the color synthesis prism 20. The
light beam incident on the color synthesis prism 20 is reflected on a
reflection surface of the color synthesis prism 20. After the reflection,
the diffraction light 25 is projected onto the screen 24 through the
projection lens 22.

[0167]In addition, as shown in FIG. 5A, in respect to light emitted from
each of the LD for red and the LD for green, the same optical system as
the optical system with respect to the light emitted from the
above-described LD for blue is provided, and diffraction light that is
related to red, green, and blue is synthesized by the color synthesis
prism 20. As a result, a full-color video image is projected onto the
screen.

[0168]In addition, as shown in FIG. 5A, the projection lens is composed of
a concave lens (negative power), but may be composed of a convex lens
(positive power). In addition, according to the above-described method,
unlike the color sequence method, a color break phenomenon does not need
to be considered.

[0169]In the SPMs 28a, 28b, and 28c, the LC and the LCOS may be used.
However, since the LC cannot increase an opening ratio, the LC has bad
light utilization efficiency. In addition, since the LCOS has low
reflectance, it is difficult to improve diffraction efficiency. However,
it is possible to overcome the above disadvantages by using an MMD, which
will be described in detail below.

[0170]In addition, with respect to the process of the video image data or
the like that has been described with reference to FIG. 3 and the on/off
control on the light sources when altering the information of the SPM
that has been described with reference to FIG. 4, the same process and
control are performed.

[0171]As described above, even when the configuration shown in FIGS. 5A
and 5B is used, it is possible to provide a holographic projection method
and a holographic projection device that can realize both video image
display having appropriate brightness and energy saving. According to the
configuration shown in FIGS. 1 and 2, the configuration of the device can
be simplified.

[0172]FIGS. 6A and 6B are cross-sectional views illustrating a reflecting
MMD that constitutes the SPMs 4a, 4b, and 4c in a holographic projection
device according to this embodiment. In the drawings, cross-sectional
views of a portion corresponding to three pixels are shown, but actually,
a plurality of pixels exist two-dimensionally. Hereinafter, the structure
of the MMD will be described with reference to FIGS. 6A and 6B.

[0173]That is, in this embodiment, an MMD 36 has a substrate 38, an
insulating layer 40, springs 42, electrodes 44, columns 46, a thin film
48, and a mirror 50.

[0174]Specifically, the insulating layer 40 is provided on the substrate
38 including a switch circuit that drives each pixel to modulate a phase.
Further, the springs 42 are provided on the insulating layer 40. In
addition, the electrode 44 that is connected to the switch circuit is
provided in a concave portion of the insulating layer 40 under each
spring 42.

[0175]In this case, in the MMD 36, as shown in FIG. 6B, the mirror 50 can
be deformed. That is, in the MMD 36, the spring 42 corresponds to each
pixel for a phase modulation, and the thin film 48 is provided above the
springs 42 in a state where the columns 46 provided on the springs 42 are
interposed between the springs 42 and the thin film 48. In addition, the
mirror 50 is integrally provided on the thin film 48.

[0176]As such, in this embodiment, the mirror 50 does not adopt the
structure where the mirror is divided to correspond to each spring 42,
but adopts a piece of board-shaped structure. By this structure, the
shape change of the mirror 50 is continuously and gradually generated.
That is, an unnecessary diffraction order can be suppressed from being
generated and diffraction efficiency can be improved.

[0177]In addition, the thin film 48 is formed of a material having
excellent flexibility and durability. The mirror 50 is formed of a
dielectric multilayer or a metal having high reflectance.

[0178]In this case, if a voltage is applied to the electrode 44, the
spring 42 becomes close to the substrate 38 by means of a Coulomb force
that is generated between the mirror 50 and the electrode 44, and the
surface of the mirror 50 is indented. The amount by which the phase of
the light reflected on the mirror 50 changes because of the indentation
is 1/4 of a wavelength. That is, in this way, it is possible to generate
a phase difference of a half-wavelength on a reciprocal path, that is,
π.

[0179]In addition, the above operation is a binary operation that only
inverts a phase. However, if a spring constant of the spring 42 is
appropriately selected, it is possible to control a strain of the spring
42 by the voltage, that is, the indentation of the mirror 50. In this
case, if the mirror 50 is controlled to have an indentation that
corresponds to half the maximum wavelength, it is possible to generate a
phase difference that corresponds to a maximum of one wavelength on a
reciprocal path. In addition, it is possible to obtain diffraction
efficiency higher than that in the binary modulation.

[0180]In addition, for example, Si is used in the substrate 38, SiO2
or SiC is used in the insulating layer 40, and a flexible metal or
conductive organic film is used in the spring 42. In addition, a
conductive material may be coated on the conductive organic film. In
addition, in the electrode 44, for example, Al, Cu, or W is used. In the
thin film 48, for example, a flexible organic film or Si2N3 is
used.

[0181]As such, it is possible to provide the SPMs 4r, 4g, and 4b having
excellent efficiency that can reflect almost 100% of the incident light
to use the mirror 50.

[0182]In addition, in regards to the binary control and the structure of
the spring 42, the technologies that are disclosed in U.S. Pat. No.
5,835,255 and U.S. Pat. No. 6,040,937 may be referred to. In these
documents, a technology that is related to an element that performs color
display using a Fabry-Perot etalon principle is disclosed.

[0183]As described above, according to the embodiment of the invention, it
is possible to provide a holographic projection device and a holographic
projection method that can realize both video image display having
appropriate brightness and energy saving with the simple configuration
and reduce speckle noise.

[0184]The present invention has been described based on the embodiment.
However, the present invention is not limited to the above-described
embodiment, and various changes and modifications can be made without
departing from the spirit and scope of the present invention.

[0185]For example, the colors of the light sources may be a combination of
three primary colors of complementary colors as long as the corresponding
colors are three primary colors that can constitute a color video image,
and is not limited to a combination of red, green, and blue.

[0186]Further, in the above-described embodiments, the invention of
various steps is included, and various inventions can be extracted from
proper combinations of the plurality of disclosed constituent elements.
For example, even if some of the constituent elements described in the
above-described embodiments are removed, when the problems described in
the problem to be solved by the invention can be solved and the effects
described in the effect of the invention can be achieved, the
configuration where some constituent elements are removed can be
extracted as the invention.